Update local CI-like testing script

[lo48576]

Current Makefile.toml is unmaintained for a while, so needs an update.

Most broken part I think is clippy lint with --deny warnings. Basically, newer clippy versions will behave better (i.e. have less false-negative and more false-positive), so failure with clippy of MSRV and stable channel are not critical if beta or nightly clippy succeeds. However, current test script requires no warnings with MSRV clippy. This is not ideal since this will reject some harmless or even better source codes.

Another problematic part is the less intuitive notation of the current Makefile.toml file.
What is @@decode(FEATURES,,,--features=${FEATURES})?
Why is it necessary to read the manual just to change condition = { rust_version = { equal = "$MSRV" } } to condition = { channels = ["nightly"] }?
How can I judge whether non-latest MSRV satisfies condition = { channels = ["stable"] } or not, without checking documentation and issue tickets?

I'd like to maintain more readable script, but still I prefer declarative ones...

[lo48576]

Note: I currently don't use online CI service (free plan) because the extensive tests for multiple toolchain versions and multiple features combinations are too heavy. They will consume time budgets very quickly.

[lo48576]

Status update: I currently own CI servers in my homelab, so I can run CI (Woodpecker) by pushing the repo to git server in the homelab.
Maybe I'll remove the almost unmaintained Makefile.toml and use it.